The present invention relates to an electronically actuated drive train in a motor vehicle, in particular in a utility vehicle, for example lorry, and a method for operating such a drive train.
A drive train usually comprises a manual gearbox, a drive unit and a power request input device. The manual gearbox can be electronically actuated with gearbox control signals. The drive unit may be, for example, an internal combustion engine which has a drive connection to the manual gearbox, and can be electronically actuated with drive control signals. The power request input device may be, for example, an accelerator pedal or a joystick, which can be activated by the driver of the vehicle, and generates power request signals. In addition, a central processing unit is assigned to the drive train. The central processing unit is connected to the power request input device, to the manual gearbox and to the drive unit, and determines drive control signals and gearbox control signals from the incoming power request signals and actuates the manual gearbox and the drive unit. In order to determine the gearbox control signals and the drive control signals, the central processing unit can access, for example, values which are stored in characteristic diagram forms and which define a predetermined gear-changing strategy.
DE 195 11 866 A1 discloses an arrangement for cyclically adapting a characteristic curve for switching gears in an automatic gearbox of a motor vehicle. In this known arrangement, correction values are determined in accordance with a switching strategy which functions by means of an algorithm which forms relationships between external influencing variables, and by evaluating measured actual values of these influencing variables. As a function of these determined correction values, the characteristic curve can then be adapted both in the direction of the coordinate which specifies a travelling-speed-dependent parameter and in the direction of the coordinate which specifies a parameter which is assigned to the engine torque.
DE 43 44 369 A1 discloses the limiting of the driving power of a vehicle drive with respect to the energy consumption. This method supports the driver in the optimum utilization of the energy supply. This is of particular significance especially for electric vehicles. At the start of a journey, a journey computer is informed of the route which is to be covered. The journey computer can then determine an acceptable route consumption by reference to the available energy supply, from which consumption a predefined value is determined taking into account driving resistances and other influencing factors. The predefined value correspondingly actuates a device for limiting the driving power. In one particular refinement of this method, the journey computer can also access a navigation system which has three-dimensional maps of the route to be covered. The journey computer then decomposes the overall route into suitable partial routes and assigns separate predefined values to them for the limitation of the driving power. In this way, for example, an increase in energy consumption for overcoming a positive gradient can be taken into account. It is of particular significance here that for the individual partial routes the known method always defines maximum values for the available driving power which must not be exceeded if the aimed-at overall route is to be covered without replenishing the energy supply.
The present invention is concerned with the problem of specifying, for an electronically actuated drive train, possible ways of reducing the energy consumption of the drive train when implementing the power request.
This problem is solved according to the invention by means of a method and a device having the features of the claimed invention.
The invention is based on the general idea of taking into account a predefinable or predefined driving style and the local position of the vehicle in the determination of the drive control signals and the gearbox control signals. The driving style can be selected from a range from minimum energy or fuel consumption up to maximum power output, or any desired compromises between these two extreme driving styles. By this driving style, it is possible to find the optimum combination of gearbox control signal and drive control signal for any power request. The current vehicle position can be matched, for example, to three-dimensional maps of the surroundings of the vehicle, that is, maps with altitude information, in order to take into account the relevant conditions. By taking into account the vehicle position, it is also possible to include route-related peripheral conditions in the determination of the combination of gearbox control signal and drive control signal which is optimized in terms of energy consumption. As a result, the energy consumption over relatively long routes can be additionally reduced. For example, it is possible to take into account the presence of a positive incline or of a negative incline of the road in the determination of the control signals.
In DE 43 44 369 A1, the driving power is limited by maximum values in a consumption-oriented fashion. The maximum values are determined from the information on the surroundings of individual partial routes of the overall route and must not be, or should not be, exceeded by the vehicle in order to cover the entire distance. In the present invention, on the other hand, the drive train is actuated from the outset in such a way that a driving style which is optimized in terms of fuel consumption is obtained within the predetermined driving style. The conditions of the more immediate surroundings are taken into account, but not the overall route which does not need to be known to the drive train according to the invention.
In a significant embodiment, the local position of the vehicle is taken into account in conjunction with three-dimensional maps of the current surroundings of the vehicle in the sense of a predictive driving style in the determination of the drive control signals and the gearbox control signals. For example, the energy or fuel consumption can be reduced by avoiding unnecessary gear changes, for example, just before a positive gradient or before a negative gradient.
Preferably, characteristic road properties, which are taken into account in the determination of the drive control signals and the gearbox control signals, can be determined from the three-dimensional maps. The following road properties, which can be taken into account cumulatively or alternatively, are of particular significance:
The distance between the current location of the vehicle and a change in the road gradient, for example, a positive gradient or a negative gradient. As already mentioned, in this way unnecessary gear changes and acceleration operations or braking operations can be avoided.
The distance between the current vehicle location and a change in the direction of the road, for example, a bend or junction. By taking into account these road properties, it is possible, for example, to avoid an unnecessary acceleration before a bend or junction if this bend or junction is assigned a maximum speed which would be exceeded by the acceleration operation.
The distance between the current vehicle position and a stopping point, for example a crossroads, a destination or an intermediate destination. Here too, unnecessary acceleration operations can be avoided in order to reduce the fuel or energy consumption.
The distance from a change in the permitted speed, for example, at an entry to a locality. Here too, the effect of taking into account this property of the road is to avoid unnecessary acceleration operations and fuel consumption.
The vehicle position can be taken into account in the determination of the drive control signals and the gearbox control signals, for example, by displacing a gear-changing time forwards or backwards. For example, when a correspondingly large positive incline is approached, it may be advantageous, even before the beginning of the incline, to select a relatively low gear in order, for example, to lose less speed in comparison to a gear-changing operation which takes place on the positive incline. As a result, the fuel consumption can be reduced.
Alternatively, or in addition, the power request of the driver of the vehicle can be smoothed and/or partially or completely ignored. The power request may be smoothed if the power request has excessive fluctuations.
Furthermore, it is possible, for example on a negative gradient, to ignore an additional power request if, for example, a permitted maximum speed has already been reached.
Likewise, it is possible to reduce the power output of the drive train before the start of a negative gradient in order to avoid or decrease braking operation for the coming negative gradient.
Furthermore, it is possible, given a constant power request, to change the power of the drive unit. In processor-controlled internal combustion engines, it is possible to increase or decrease the parameters relating to power by adjusting the control. For example, this can be done by changing the injection quantity, the injection pressure, the injection time, the position of the throttle valve, the ignition time by activating or deactivating individual cylinders and the like. For example, it may be appropriate to select the drive power of the drive train as a function of the current weight of the vehicle. A lorry, which is configured for transporting a load of 40 tonnes, has too much drive power in the unloaded state and is “overpowered”. By reducing parameters of the engine power electronically, the power can be balanced in order to reduce the consumption of fuel. Likewise, it is possible to briefly increase the parameters of the power of the internal combustion engine in order to overcome relatively large positive gradients.
It goes without saying that the features which have been mentioned above and are to be explained below can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.